Since the discovery of penicillin in the 1920s and streptomycin in the 1940s, many new compounds have been discovered or specifically designed for use as antibiotic agents. It was once believed that infectious diseases could be completely controlled or eradicated with the use of such therapeutic agents. However, such beliefs have been shaken because strains of cells or microorganisms resistant to currently effective therapeutic agents continue to evolve. In fact, virtually every antibiotic agent developed for clinical use has ultimately encountered problems with the emergence of resistant bacteria. For example, resistant strains of Gram-positive bacteria such as methicillin-resistant staphylococci, penicillin-resistant streptococci, and vancomycin-resistant enterococci have developed. These resistant bacteria can cause serious and even fatal results for patients infected with such resistant bacteria. Bacteria that are resistant to macrolide antibiotics have emerged. Also, resistant strains of Gram-negative bacteria such as H. influenzae and M. catarrhalis have been identified. See, e.g., F. D. Lowry, “Antimicrobial Resistance: The Example of Staphylococcus aureus,” J. Clin. Invest., vol. 111, no. 9, pp. 1265-1273 (2003); and Gold, H. S, and Moellering, R. C., Jr., “Antimicrobial-Drug Resistance,” N. Engl. J. Med., vol. 335, pp. 1445-53 (1996).
The problem of resistance is not limited to the area of anti-infective agents. Resistance has also been encountered with anti-proliferative agents used in cancer chemotherapy. Therefore, the need exists for new anti-infective and anti-proliferative agents that are both effective against resistant bacteria and resistant strains of cancer cells.
Despite the problem of increasing antibiotic resistance, no new major classes of antibiotics have been developed for clinical use since the approval in the United States in 2000 of the oxazolidinone ring-containing antibiotic, linezolid, which is sold under the trade name Zyvoxe®. See, R. C. Moellering, Jr., “Linezolid: The First Oxazolidinone Antimicrobial,” Annals of Internal Medicine, vol. 138, no. 2, pp. 135-142 (2003). Linezolid was approved for use as an anti-bacterial agent active against Gram-positive organisms. However, linezolid-resistant strains of organisms are already being reported. See, Tsiodras et al., Lancet, vol. 358, p. 207 (2001); Gonzales et al., Lancet, vol 357, p. 1179 (2001); Zurenko et al., Proceedings Of The 39th Annual Interscience Conference On Antibacterial Agents And Chemotherapy (ICAAC), San Francisco, Calif., USA (Sep. 26-29, 1999).
Another class of antibiotics is the macrolides, so named for their characteristic 14- to 16-membered ring. The macrolides also often have one or more 6-membered sugar-derived rings attached to the main macrolide ring. The first macrolide antibiotic to be developed was erythromycin, which was isolated from a soil sample from the Philippines in 1952. Even though erythromycin has been one of the most widely prescribed antibiotics, its disadvantages are relatively low bioavailability, gastrointestinal side effects, and a limited spectrum of activity. Another macrolide is the compound, azithromycin, which is an azolide derivative of erythromycin incorporating a methyl-substituted nitrogen in the macrolide ring. Azithromycin is sold under the trade name Zithromax®. A more recently introduced macrolide is telithromycin, which is sold under the trade name Ketek®. Telithromycin is a semisynthetic macrolide in which a hydroxyl group of the macrolide ring has been oxidized to a ketone group. See Yong-Ji Wu, Highlights of Semi-synthetic Developments from Erythromycin A, Current Pharm. Design, vol. 6, pp. 181-223 (2000), and Yong-Ji Wu and Wei-uo Su, Recent Developments on Ketolides and Macrolides, Curr. Med. Chem., vol. 8, no. 14, pp. 1727-1758 (2001).
In the search for new therapeutic agents, researchers have tried combining or linking various portions of antibiotic molecules to create multifunctional or hybrid compounds. Other researches have tried making macrolide derivatives by adding further substituents to the large macrolide ring or associated sugar rings. However, this approach for making macrolide derivatives has also met with limited success.
Notwithstanding the foregoing, there is an ongoing need for new anti-infective and anti-proliferative agents. Furthermore, because many anti-infective and anti-proliferative agents have utility as anti-inflammatory agents and prokinetic agents, there is also an ongoing need for new compounds useful as anti-inflammatory and prokinetic agents. The present invention provides compounds that meet these needs.